Lubricant composition containing a tin compound



United States Patent 3,490,738 LUBRICANT COMPOSITION CONTAINING A TIN COMPOUND John R. Stemniski, Swampscott, Mass., assignor to Monsanto Research Corporation, St. Louis, Mo., a corporation of Delaware N0 Drawing. Original application Sept. 19, 1963, Ser. No. 310,129. Divided and this application Dec. 7, 1967, Ser. No. 733,724

Int. Cl. Cm 1/54 U.S. Cl. 25249.7 8 Claims ABSTRACT OF THE DISCLOSURE A lubricant comprising a polyphenyl ether base fluid and a stabilizing amount of a disubstituted tin compound of the following formula:

Where each R and R is a substituent selected from aryl and aryloxyaryl radicals having from 2 to 3 benzene rings and n is an integer with a value of at least 1.

This is a division of application Ser. No. 310,129 filed Sept. 19, 1963.

This invention relates to fluids of high thermal stability, and more particularly, provides functional fluids comprising polyphenyl ethers and certain tin compounds as additives therefor. The invention also provides certain novel disubstituted tin compounds.

Polyphenyl ethers have found wide application as functional fluids owing to their very good thermal stability, lubricity, and resistance to foam. For example, they have been found to be valuable as hydraulic fluids, as heatexchange media, as atomic reactor coolants, as diffusion pump fluids, as lubricants in motor operation generally, and particularly as jet engine lubricants.

As is known in the art, petroleum lubricants, in addition to the petroleum base stock, generally include additives which impart specific desired properties to the base stock, such as rust inhibitors, anti-oxidants, extreme pressure resisting agents, lubricity improvers, detersives and the like. The additives proposed heretofore have been designed to provide petroleum base compositions for lubrication in conventional equipment such as internal combustion engines of the automotive type, diesel engines and the like, in which the temperature of use is not excessive, not exceeding about 400 F. Advanced designs such as jet aircraft design have called for effective lubrication at higher temperatures, such as 500 F. and above, and for these designs, it was found that neither the petroleum base stock nor the conventional additives used therewith were practical. The temperatures of operation exceeded the boiling point of some lubricant composition components, and generally were in a range at which both lubricant and additives were thermally unstable and decomposed.

Development of synthetic base stocks like the polyphenyl ethers has provided lubricant fluids stable at temperatures above the useful range of the mineral oils. There is now a demand for compositions in which such functional fluids, with thermal stability superior'to that of the mineral oils, are compounded with additives enhancing desirable properties thereof. Many materials known as useful mineral oil additives are, as stated, excluded from utility in this connection by volatility and lack of thermal stability at the temperatures of use of the polyphenyl ethers. Furthermore, it has been found that additives conventional in mineral oil lubricants do not perform predictably upon combination with synthetic 3,490,738 Patented Jan. 20, 1970 base stocks. There are significant differences in chemical structure of the stocks which can affect the response to additives: for example, Whereas the mineral oils consist of aliphatic hydrocarbons, the polyphenyl ethers are, by contrast, aromatic ethers. Indeed, base stocks chemically different from the mineral oils may actually suffer chemical attack by certain additives, with deleterious effects on their superior high temperature properties. Temperature of operation can also affect the performance of additives, and so forth. Thus an empirical approach has been required for the provision of improved lubricants including the polyphenyl ethers as base stocks.

Although the polyphenyl ethers possess extremely good thermal stability, at temperatures of, say, over 550 F., they tend to deteriorate, not because of a decomposition reaction, but because at the higher temperatures they become quite readily oxidizable. The lubricity of the polyphenyl ethers is thereby impaired, since the oxidation products do not possess lubricating properties; moreover, the change in viscosity which is a consequence of the oxidation not only makes for inefliciency, but also may result in clogging up the moving parts of the mechanism which the lubricant was originally intended to protect. Hence, when the polyphenyl ethers are to be used at the higher temperatures under conditions requiring exposure to air, it is important to inhibit oxidation phenomena which the higher temperatures favor.

An object of the present invention is the provision of improved lubricant compositions employing polyphenyl ether fluids as base stock.

A particular object of the present invention is to provide polyphenyl ether base compositions having improved oxidation resistance.

Another object is to provide novel tin compounds useful as antioxidants for polyphenyl ether base fluids.

These and other objects will become evident upon consideration of the following specification and claims.

It has now been found that compositions consisting essentially of a polyphenyl ether base fluid and an additive amount of a disubstituted tin compound of the formula [R SnR where each of R and R is an aromatic radical containing at least two aromatic rings, and n is an integer which has a value of at least one, have improved ability to resist oxidation degradation at high temperatures.

The stated tin compounds are disubstituted tin compounds, which may be either monomeric or polymeric. In general, the monomeric divalent tin compounds readily polymerize on standing: the polymers, which are compounds of the stated formula [R SnR where n is an integer greater than one, may have a cyclic structure, such as Sn R2 l R2 and in general appear to be low polymers, where n has a value of, say, up to 10.

For the present purposes, the useful disubstituted tin compounds are those with two organic substituents which each are selected from aryl and aryloxyaryl radicals, and contain from 2 to 3 benzene rings. The stated aryl radicals will be aromatic hydrocarbon radicals. The benzene rings may be separate or fused. Illustrative of the presently useful diaryl tin compounds are dibiphenylyltin, dinaphthyltin, dianthryltin, diphenanthryltin, diacenaphthyltin, diterphenylyltin, biphenylyl naphthyltin and the like. Presently useful aryloxyaryl tin compounds, which are particularly preferred in the practice of this invention,

are exemplified by bis(phenoxyphenyl)tin, bis (biphenylyloxyphenyl tin, bis (phenyloxybiphenylyl tin, bis (naphthyloxyphenyl) tin, (biphenyloxyphenyl) (phenoxyphenyl)tin and so forth. It is to be understood that the listing above of the diorganotin compounds without designation of particular isomers is intended to be inclusive of each isomer; for example, di-o-, di-mand di-p-biphenylyltin, di-aand di-fl-naphthyltin, and so forth. Also, in referring to these disubstituted tin compounds without more, in the absence of specification to the contrary, both the monomeric and polymeric forms are intended to be included.

As is known, the diaryltin compounds are prepared by a Grignard synthesis. The bis(aryloxyaryl) tin compounds of the above-stated nature, which are a novel class of compounds provided hereby, are prepared similarly, by reaction of an aryloxyaryl magnesium halide with a tin dihalide:

where each of R and R represents an aryloxyaryl radical in which aryl is an aromatic hydrocarbon radical, and rt is an integer which is at least 1. Exemplary of useful Grignard reagents are p-phenoxyphenylmagnesiurn bromide, m-phenoxyphenylmagnesium bromide, p-(p-biphenylyloxy)phenylmagnesiurn bromide, p c naphthyloxyphenylmagnesium bromide, and so forth. The conditions for the reaction are generally like those known for preparation of the diaryltin compounds: the starting materials are contacted, in approximately equimolar quantities (2 moles total of Grignard reagent per mole of tin dichloride), under anhydrous conditions, in an organic solvent. This may be an acyclic ether, such as diethyl ether, the dimethyl ether of ethylene glycol, or the like; cyclic ethers such as tetrahydrofuran are advantageous and are preferred. Generally the reaction mixture is heated to temperatures of 50--150 C., the reflux temperature of the reaction mixture is usually suitable. After completion of the reaction, the product is recovered by conventional procedures: filtration, evaporation to remove solvent, and so forth. In general, the polymeric form is produced spontaneously upon standing of the freshly prepared monomeric product.

The polyphenyl ethers employed in the fluid compositions of this invention have from 3 to 7 benzene rings and from 1 to 6 oxygen atoms, with the stated oxygen atoms joining the stated benzene rings in chains as ether linkages. One or more of the stated benzene rings in these polyphenyl ethers may be hydrocarbyl-substituted. The hydrocarbyl substituents, for thermal stability, must be free of CH and aliphatic CH, so that preferred aliphatic substituents are lower saturated hydrocarbon radicals (1 to 6 carbon atoms) like methyl and tert-butyl, and preferred aromatic substituents are aryl radicals like phenyl and tolyl. In the latter case, the benzene ring supplied in the hydrocarbyl substituent contributes to the total number of benzene rings in the molecule. Polyphenyl ethers consisting exclusively of chains of from 3 to 7 benzene rings with at least one oxygen atom joining the stated benzene rings in the chains as an ether linkage have particularly desirable thermal stability.

Exemplary of the alkyl polyphenyl ethers suitable for base fluids are 3-ring polyphenyl ethers like l-(p-methylphenoxy)-4 phenoxybenzene and 2,4-diphenoxy-1-methylbenzene, 4 ring polyphenyl ethers like bis[p-(p-methylphenoxy)phenyl] ether and bis[(p-tert-butylphenoxy) phenyl] ether, and so forth.

Polyphenyl ethers consisting exclusively of benzene rings and ether oxygen atoms linking said rings are exemplified by the triphenoxy benzenes and aryl-substituted polyphenyl ethers such as biphenylyl phenoxyphenyl ether, biphenylyloxyphenyl phenoxyphenyl ether, biphenylyl ether, dibiphenylyloxybenzene, bis,(phenylyloxyphenyl) ether, and the like.

A preferred class of polyphenyl ethers comprises those consisting of benzene rings joined in a chain by oxygen atoms as ether linkages between each ring.

Examples of the polyphenyl ethers contemplated in this class are the bis(phenoxyphenyl) ethers (4 benzene rings joined in a chain by 3 oxygen atoms), illustrative of which is bis(m-phenoxyphenyl) ether. The bis(-phenoxyphenoxy)benzenes are particularly valuable in the present connection. Illustrative of these are m-bis(m-phenoxy phenoxy)benzene, m-bis(p-phenoxyphenoxy)benzene, obis(o-phenoxyphenoxy)benzene, and so forth. Further, the polyphenyl ethers contemplated herein include the bis(phenoxyphenoxyphenyl) ethers such as bis[m-(mphenoxyphenoxy)phenyl] ether, bis[p (p phenoxyphenoxy)phenyl] ether, m (m phenoxyphenoxy)phenyl rn-(o-phenoxyphenoxy)phenyl ether and the his (phenoxyphenoxyphenoxy benzenes such as rn-bis[m-(.m-phenoxy phenoxy phenoxy] benzene, p-bis [p- (m-phenoxyphenoxy) phenoxy]benzene and m bis[m (p phenoxyphenoxy) phenoxy]benzene.

The preferred polyphenyl ethers are those having all their ether linkages in the meta-positions since the allmeta-linked ethers are particularly advantageous because of their wide liquid range and high thermal stability. However, mixtures of the polyphenyl ethers, either isomeric mixtures of mixtures of homologous ethers, can also advantageously be used in some applications, especially where particular properties such as lower solidification points are required. Mixtures of polyphenyl ethers in which the non-terminal phenylene rings are linked through oxygen atoms in the meta and para positions have been found to be particularly suitable to provide compositions with wide liquid ranges. Of the mixtures having only meta and para linkages, a preferred polyphenyl ether mixtures of this invention is the mixture of 5 ring polyphenyl ethers wherein the nonterminal phenylene rings are linked through oxygen atoms in the meta and para position, and composed by weight of about 65% mbis(m-phenoxyphenoxy)benzene, 30% m [(m phenoxyphenoxy) (pphenoxyphenoXy)l benzene and 5% mbis(p-phenoxyphenoxy)benzene. Such a mixture is liquid at room temperature (about P.) where as the three components solidify individually at temperatures above normal room temperatures.

The aforesaid polyphenyl ethers can be obtained by known procedures such as, for example, by the Ullmann ether synthesis, by a procedure involving reaction of alkali metal phenoxides such as sodium and potassium phenoxides with aromatic halides such as bromobenzene in the presence of a catalyst such as metallic copper, copper hydroxides or copper salts.

The disubstituted tin compound is combined with the fluid polyphenyl ether base fluid to the extent of, generally, between about 0.01% and 10% by weight of the fluid. Particular effective amounts depend on the nature of the individual additive and of the ether fluid; lowering the concentration sometimes enhances antioxidant effects. For purposes of supplying additive concentrates, adapted for convenient formulation of finished lubricant composition, useful compositions may comprise up to about a 1:1 weight ratio of the additives of this invention and the polyphenyl ether base fluid.

It will be appreciated that the compositions of this invention, in addition to the polyphenyl ether base fluid and the tin compound, may additionally include any of a wide variety of further additives. For example, these may include sludge inhibitors and detergents such as the oilsoluble petroleum sulfonates, to loosen and suspend products of decomposition and counteract their effect. Other agents such as viscosity index improvers, as exemplified by alkyl methacrylate polymers, pour point depressants oiliness agents, and so forth, may also be present in these compositions if desired.

The invention is illustrated but not limited by the followin examples.

EXAMPLE 1 This example illustrates preparation of a bis(aryloxyaryl) tin compound as provided by this invention.

p-Phenoxyphenylmagnesium bromide is prepared in the usual manner using 50 grams (g.) (0.20 mole) of p-bromophenyl phenyl ether and 4.86 g. (0.20 g.-atom) of magnesium using tetrahydrofuran as solvent. To theGrignerd reagent is added 18.9 g. (0.1 mole) of stannous chloride (anhydrous) dissolved in 150 milliliters (ml.) of tetrahydrofuran. The mixture is refluxed for two hours and cooled. About 65 ml. of saturated ammonium hydroxide solution is added and the mixture is filtered. The filtrate is reduced to dryness. The yellow viscous oil obtained solidifies on standing: the compounds as formed initially is identified as monomeric bis(phenoxyphenyl)tin, and the solid formed on standing, as polymeric bis(phenoxyphenyl)tin.

EXAMPLE 2 This example provides an illustration of the improved oxidation stability of compositions of this invention as compared to the base fluid in the absence of additive.

A lubricant composition is prepared by combining disubstituted tin compounds, as set forth below, with a polyphenyl ether of the following composition, by weight, 65% m-bis(m-phenoxyphenoxy)benzene, 30% m-[(m phenoxyphenoxy)-(p-phenoxyphenoxy)Jbenzene, 5% mbis p-phenoxyphenoxy benzene.

For determination of the antioxidant effect of the presently employed additives, air is bubbled through duplicate samples at 600 F. for 24 or 48 hours at a rate of 1 liter per hour of air, in the presence and absence of Fe, Cu, Al and Ag wires. The percent change in viscosity (at 100 F.) from before to after oxidation is an index of antioxidant activity.

Portions of the stated polyphenyl ether are combined, respectively, with the monomeric and with the polymeric, solid bis(phenoxyphenyl)tin product made as described in Example 1, each in a proportion of 1 g. of the tin compound to 100 g. of the base fluid.

A portion of the base fluid used to provide the abovedescribed composition is reserved, free of additive, and the stated compositions and the sample of the base fluid without additive are subjected to the above-described oxidation test, conducted with and without the presence of wires of Fe, Ag, Cu and A1, with the following results:

Percent Viscosity Increase, cs. at 100 F.

In Absence In the same oxidation test, using a composition pre pared by combining the stated polyphenyl ether base fluid with di-9-phenanthryltin in a proportion of 0.25 g. per g. of base fluid, a reduction in viscosity increase is also obtained as compared to the base fluid:

While the invention has been described with reference to specific preferred embodiments thereof, it is to be appreciated that modifications and variations can be made without departing from the scope of the invention, which is limited only as defined in the appended claims.

What is claimed is:

1. A lubricant composition consisting essentially of a polyphenyl ether base fluid and a stabilizing amount of a disubstituted tin compound of the formula wherein each of R and R is a substituent selected from the class consisting of aryl and aryloxyaryl radicals containing from 2 to 3 benzene rings, wherein each said aryl radical is an aromatic hydrocarbon radical and n is an integer with a value of at least one.

2. The composition of claim 1 wherein said tin compound is a monomeric disubstituted tin compound.

3. The composition of claim 1 wherein said compound is a polymeric disubstituted tin compound.

4. The composition of claim 1 wherein said tin compound is a diaryltin.

5. The composition of claim 4 wherein said tin compound is diphenanthryltin.

6. The composition of claim 2 wherein said tin compound is a bis(aryloxyaryl)tin.

7. The composition of claim 6 wherein said tin compound is his (phenoxyphenyl)tin.

8. The composition of claim 7 wherein said tin compound is monomeric.

References Cited UNITED STATES PATENTS 2,334,566 11/1943 Lincoln 252-49.7 X 3,010,979 11/1961 Ramsden 260-4297 3,245,907 4/1966 Stark et a1 25249.7 X 3,357,920 12/1967 Nacson 25249.7 X 3,389,157 6/1968 Ramsden 26045.75 X

DANIEL E. WYMAN, Primary Examiner W. CANNON, Assistant Examiner US. Cl. X.R. 

